The field of the present invention is devices that meter and dispense singular and plural component liquids and solids.
Systems for mixing and dispensing singular and multi-component materials are well known in the art. An almost infinite variety of substances may be dispensed. Many materials are packaged through dispensing in a fluid or semifluid state. Paint is sprayed, molds are pressure charged with materials, and electronic devices are potted. A variety of means for distributing such materials are available. Where plural components are involved, such systems typically include pumping mechanisms for pumping and metering separate materials in a prescribed ratio to a mixing device that thoroughly mixes these materials together. The mixed composition then flows out of a dispensing nozzle directly to the surface or point of application where the composition is desired.
When a curable composition is desired, two or more suitable materials are mixed to interact with each other to create a flowable, curable composition which will set or harden to a non-flowable state. The time required for a curable composition to harden is referred to as the xe2x80x9ccurexe2x80x9d time and often is a short period of time. Such resulting curable compositions have been used, for instance, as adhesives, sealants and potting materials in a wide variety of industrial applications and for the creation of useful objects.
Production environments can impose limitations on how a dispensing device should operate. For example, in a production environment, it is desirable for the curable composition to cure as rapidly as possible so that subsequent production operations can be performed on the production item without having to wait a significant time for curing to occur.
Further, production requirements often include the need to dispense a precise amount of a properly constituted composition. A deviation in the actual ratio of the constituent materials dispensed may alter the strength, viscosity, cure time and/or other properties and attributes of the composition. Thus, a dispensing system should dispense the desired ratio and quantity of constituent materials as accurately as possible. In many cases, the desired ratio is expressed as a function of the weight or mass of two constituent components. Nonetheless, the two constituent components are generally supplied to the mixer by volumetric metering pumps which control the volumetric ratio of the two components, rather than their weights or masses. The volumetric ratio fails to account for any changes in density and changes in mass that may occur when the components are subjected to temperature or pressure change.
Also, production items often move along a production line at a set speed. Therefore, the flow rate of the dispensed composition should be kept or maintained as constant as possible so that the time required to dispense the proper amount of composition onto or into the production item remains constant.
An assembly line operation may further require that the composition be dispensed intermittently because the composition is applied to production items that are separated spatially and temporally. Dispensing compositions intermittently may cause a loss of flow control and/or ratio control. During the first few seconds of dispensing a composition, a transient imbalance phenomenon may arise from the elasticity of materials in the dispensing system and/or changing pressures caused by cycling the dispenser. When pressure changes, the volume of stored material between the mixer and the pump changes. In other words, changes in pressure may introduce an error into the weight or mass ratio of the constituent components because a higher pressure results in a component taking less volume than the component would otherwise take, or in an expansion or shrinkage of the hoses, fittings and tubes. The loss of control may result in inaccurately dispensed quantities or ratio of materials. This loss of flow control can occur separately or in addition to the loss of ratio control. A loss of ratio control occurs when the transient imbalance phenomenon causes the dispensing system to dispense too much or too little of one constituent material, thereby resulting in an improperly constituted end product. In other words, even if the ratio control is not lost during the early stage of dispensing a composition, the flow control may be lost. Therefore, it is desirous to control both the ratio of constituent materials and the flow rate of dispensing of the resulting composition.
Dispensing machines may be used to create various types of compositions. A dispensing machine may be required to dispense two or more constituent materials to form a first composition and then switch to dispense either the same constituent materials in a different ratio or other constituent materials to form a second composition. Thus, it is desirable for a dispensing machine to change what materials are dispensed, the quantities of materials dispensed and/or the ratio of constituent materials while maintaining the ability to control accurately the quantity, ratio, flow rate and other dispensing criteria. Current dispensing systems fail to satisfy these needs and require users to shut down the dispensing machine and go through a lengthy calibration cycle in order to adjust the machine to the viscosity and/or other properties of the constituent materials.
Some dispensing systems include vats capable of holding large amounts of a constituent material. Motor-driven agitators are placed inside the vat to maintain the material homogeneity. One system is illustrated in U.S. Pat. No. 5,857,589, the disclosure of which is incorporated herein by reference. This system employs progressive cavity pumps and provides a system upon which the present disclosure is based and is prior art to the present invention.
The present invention is directed to dispensing systems employing progressive cavity pumps and controlled motor operation.
In a first separate aspect of the present invention, a dispensing system includes a valved nozzle to dispense material from a progressive cavity pump. The nozzle does not directly control the pump. Rather, a pressure sensor senses flow pressure in the system. This pressure is impacted upon by operation of the remote nozzle. A controller responds to pressure build up or decay and controls the pump accordingly.
In a second separate aspect of the present invention, the first separate aspect is further contemplated to define preselected pressures for actuation of the controller. Other attendant features are contemplated in this context. Compressed air may be supplied to the nozzle for the system to act as a paint sprayer, for example. The device might include multiple progressive cavity pumps for the mixing of separate flowable materials. With multiple progressive cavity pumps, the pumps preferably operate together to dispense multiple flowable materials and run at preselected proportional speeds relative to one another to create the proper mix. The system may be configured with one or more drum rams. The progressive cavity pumps can be mounted at the drum rams to reduce suction head requirements and to avoid difficulties with portable hoses and the like.
In a third separate aspect of the present invention, a method for spraying is contemplated which includes a repeated sampling of pressure in the system. A nozzle is opened and closed as material is needed without direct feedback from the dispensing value or nozzle. Pressure in the flow system is monitored and the progressive cavity pumps are driven responsive to the state of the pressure. When the method is also applied to accurate mixing, the motors are controlled simultaneously and provide preselected proportional pump speeds for mixture control.
In a fourth separate aspect of the present invention, a method for maintaining a stable set of operating conditions in a progressive cavity pump with the outlet closed includes periodically rotating the progressive cavity pump first in one direction and then in the other through a partial turn. The second rotation may also be varied from that of the associated first rotation as a function of pressure change. This may be done incrementally based on the pressure response occurring in the prior complete cycle or on direct pressure feedback.
In a fifth separate aspect of the present invention, the fourth aspect further includes the monitoring of system integrity by measuring pump absolute radial position after each cycle, continued advancing pump position being indicative of a leak in the system.
In a third separate aspect of the present invention, a high flow rate dispensing system using progressive cavity pumps includes a releasably coupled manifold to the pump supply lines. The manifold includes one passage extending into a discharge concentrically within the other passage. A mixer further combines the two flows. Valves may be employed to accommodate large flow rates and complete shut off.
In a fourth separate aspect of the present invention, a timer cooperates with a signal generator in a pumping system to provide a warning when the material in the system is approaching set up such that it cannot be driven through the system. Where a curable composition is being pumped and mixed, it will set or harden in a nonflowable state. Avoidance of this condition within the dispensing equipment is advantageous.
In a fifth separate aspect of the present invention, one or more progressive cavity pumps are controlled to provide virtual stall operation. A drive torque relationship with pressure is determined for specific speeds. When the torque approaches or exceeds a pre-established value for a specific speed, indicative of reaching a preset pressure limit, torque is limited.
In a sixth separate aspect of the present invention, various combinations of the foregoing aspects are contemplated to provide system advantage.
Accordingly, it is an object of the present invention to provide improved systems and methods for accurately dispensing flowable material. Other and further objects and advantages will appear hereinafter.